1. Field of the Invention
This invention relates to a method of forming plastic composite material, and more particularly to a method of forming to shape plastic products by composite material combining fiber reinforced plastic material with a thermosetting resin.
2. Description of the Prior Art
For producing plastic products of circular shapes or channel materials of I- and V-shapes in section by molding a plastic mat material reinforced with fiber such a carbon fiber aramid fiber or glass fiber, there has been known a method of impregnating a thermosetting resin into a plastic mat material while passing the same continuously through a heated mold and thermosetting the plastic mat and the resin.
In this conventional method, a composite material mat is firstly formed by plying woven fabric of carbon fiber or the like and rovings of carbon fiber and glass fiber in multiple layers, followed by needle punching.
Nextly, the composite material mat is pressed into a heated mold while simultaneously injecting a thermosetting resin into the heated mold, thermosetting the resin-impregnated mat and simultaneously drawing the same continuously out of the mold to obtain the molded product.
In the above-described conventional method, a great frictional force occurs between the mold and the material which is being formed into a predetermined shape by the drawing operation.
In order to lessen this frictional force, it has been a compulsory requisite to employ a polyester resin with a small frictional coefficient though low in strength. However, recent improvements to the forming method have made it possible to use epoxy resins of high strength in spite of a large frictional coefficient.
An advantage of the products which are obtained by this forming method resides in that they have high strength per weight, permitting to provide products of given strength in a smaller weight as compared with, for instance, products of light alloy materials. Consequently, the products of this forming method are considered to be suitable for application to structural materials for transportation equipments including structural materials for aircrafts.
However, the application of the products of the conventional molding method as aircraft structural materials involves the following problems to be solved.
(1) The weight ratio of fiber to resin is 60% to 40%, that is to say, the fiber proportion is too small, so that it is difficult to obtain a product of high strength.
(2) The resin has to be thermally set within a relatively short period of time while the material is being passed through the heated mold, so that it is difficult to obtain a product of uniform strength through controlling thermosetting reaction.
(3) The great frictional force which occurs between the mold and the material during the molding process necessitates to apply a lubricant on the surfaces of the mold.
(4) The release material which is mixed with the resin during the molding process remains on the surfaces of the products.
The residue of the release material on the surface of the product makes it difficult to apply an adhesive thereto or to bond the product to other components.
(5) The composite material mat is shaped by forcibly drawing the same through a mold, so that the fiber on the surface of the material is apt to be dragged and aligned in the drawing direction (in the longitudinal direction) by the frictional contact with the mold surface, encountering the difficulty in molding the material such that the fiber layers are plied with a fiber inclination of 45 degrees with respect to the drawing direction.
Therefore, it has been almost impossible to control the torsional strength of the products.
One of the causes of the above-mentioned problems is considered to be the manner of pressing the material in the molding process. Pressure is applied to the material in the molding stage for smoothing the surface of the product and uniformalizing the product quality.
As means for producing the pressing force, the conventional molding method forms a mat by interposing roving and non-woven fabric in layers between fibrous woven fabric to utilize the reaction force of the roving and non-woven fabric as the mat is squeezed into the mold.
Therefore, it has been difficult to obtain a large pressure force and to increase the proportion of the fibrous woven fabric in the mat which is composed of the fibrous woven fabric, roving and non-woven fabric. Since the strength of the product is mainly imparted by the woven fabrics of carbon and glass fibers, products of extraordinarily high strength have been difficult to make for the reasons stated above.
In addition, as the drawing operation is performed under the pressurized state, the use of a release material has been inevitable in order to lessen the large friction which occurs between the mold and the product.
Further, the conventional forming method which resorts to the drawing operation for shaping the material is restricted to linear products alone.